Thread trimming device for lockstitch sewing machines

ABSTRACT

A thread trimming device for a lockstitch sewing machine in which a thread pull-off arm, a thread catching arm, and a thread cutting blade are swung at different distances back and forth transversely of the face of a lockstitch forming loop taker by a novel arrangement of cam means on the sewing machine whereby the trimmer elements may move across the paths of prominences of the loop taker but without interference with the loop taker.

UNITED STATES PATENTS 5/1970 Heimann et a1. 112/252 O I Umted States Patent [1 1 [111 3,776,161

Papajewski et al. Dec. 4, 1973 [5 THREAD TRIMMING DEVICE FOR 3,141,432 7/1964 Reeber 6: a1. 112 252 LOCKSTITCH SEWING MACHINES 3,173,392 3/1965 Hedegaard 3,443,540 5/1969 Hannemann et a1 112/252 Inventors Rernhold p i Johann 3,605,664 9/1971 Hedegaard 112/252 Kleinschmidt, both of Buechig, Y Germany Primary Examiner-Werner H. Schroeder [73] Assignee: Singer-Werke GmbH, Blankenloch, Attorney Marshau Bree et 7 Germany 22 Filed: Aug. 9, 1972 [57] ABSTRACT A thread trimming device for a lockstitch sewing ma- [21] Appl' 278906 chine in which a thread pull-off arm, a thread catching arm, and a thread cutting blade are swung at different 52 US. Cl. 112/252 distances back a forth transversely of the face of a 51 Int. Cl D05b 65/02 leekstiteh forming p taker y a novel armngernent [58] Field of Search 112/252 of earn means on the ng machine whereby the r trimmer elements may move across the paths of prom- 5 R f r it inences of the loop taker but without interference with the loop taker.

4 Claims, 9 Drawing Figures THREAD TRIMMING DEVICE FORLOCKSTITCI-I SEWING MACHINES BACKGROUND OF THE INVENTION SUMMARY OF THE-INVENTION It is an object of the present invention tovprovide an underbed needle and bobbin thread trimmer for a lockstitch sewing machine including a threadcutting' blade, and thread catching and bobbin thread pull-off which can be shifted transversely of the face of the looptak'er across the path of movement of prominences on the loop taker so as to provide a particularly compact thread trimmer which occupies a minimu-mof the critical space available in the vicinity of the loop taker.

A sequence of movements of the'variouselements-of the thread trimming mechanismto avoid physicalinterference with movement of the loop taker prominences is attained in this invention by a novelarrangement of a plurality of trimmer actuating cams and a mechanism for responding in sequence to the actuating cams. This invention provides a thread trimming: mechanism which occupies a minimum of space in the vicinity of the'loop taker and which can be readily applied to any one of a wide variety oflockstitch'sewing machine constructions.

DESCRIPTION OF THE DRAWINGS stantially along line 2--2 of FIG. 1 showing the primary trimmer actuating cam, I

FIG. 3 is a side elevational view mer actuating cam of FIG. 2,

FIG. 4 is an enlarged cross-sectional view taken substantially along line 4--4 of FIG. 1 showing both the primary and secondary thread trimmer actuating cams together with the respective cam followers,

FIG. 5 is a perspective view of the thread engaging elements of the thread trimming mechanism,

FIG. 6 is an enlarged cross-sectional 'view of the sewing machine bed taken substantially along linc 66of FIG. 1 showing the inoperative position of'the thread trimmer elements,

FIG. 7-is a view of the thread trimmer elements similar to that shown in FIG. 6 but showing the first'movement of the thread catching and thread pull-off armsin response to the primary actuating cam,

FIG. MS a view of the thread trimming elements similar to that shown in FIG. 7 but showing thethread cutting blade and thread pull-off arm inthe extreme positions to which they are shifted by the secondary actuating cam, and

of the primary trim- FIG 9 is a view of the thread trimming elements similar to that shown in FIG. 8 but. showing the thread catch-ing arm in the thread severing position into which it is shifted by the primary actuating cam.

As shown in FIGS. 1 and 6, 11 is a work supporting bed of a sewing machine frame. A loop taker indicated generally at 12 is supported in the bed and serves to concatenate needle thread with thread issuing from .a bobbin 13 held in a bobbin case 14 within the loop taker in the formation of lockstitches. The loop taker may take the form of that disclosed and described in greater detail in the US. Pat. No. 2,085,699, June 29, 1937 to which reference may bebad. This loop taker is referred to in the art as a rotary hook and includes 5 a needle thread seizing beak 15 which may extend from the rim 16 of a cup-shaped body within which the bobbin case 14 is constrained. A peripheral thread pull-off rib 17 is attached to the hook body rim 16 in a conventional manner. The thread pull-off rib l7, hook rim l6, and bobbin case 14 are each irregularly formedon the exposedface of the hook and may include axial projections which have significance in the manipulation of the threads during stitch formation.

Alongside the loop taker l2 and secured on a web 20 of the work supporting bed 11 as by a fastening screw 21 is a support block 22 for the movable thread influen'cingm'embers of the thread trimming mechanism of this invention. Pivoted on a common fulcrum stud 23 secured in the support block 22 are a pair of bell crank levers 24 and 25. A thread cutting blade 26 embraces a pin 28 projecting from one arm of the bell crank lever 24" and is secured with capacity for a limited range of adjustment about the pin 28 by a fastening screw 2). The extremity of the bell crankxlever 24 is recessed as at 30 and a'clamp screw 31 threaded into the bell crank lever in this recess can 'be used to deflect the thread cutting blade-toregulate the cutting position thereof.

A thread catching arm 40 which is secured to one arm'of the bell crank-lever 25 by a fastening screw 41 is formed, as shown in FIGS. 5 and 6, with a flattened v heel portion42 which overlaps and can engage the bell crank 24. The free extremity of the thread cutting blade 26 is formed with a sharpened cutting edge 43, and the free extremity of the thread catching arm 40 as shown'in FIG. 5, is formedwith a laterally extending thread engaging hook 44' suitable for catching and drawing threads across the cutting edge 43.

' In'the retracted position of the thread cutting blade 26; the bell crank 24 abuts a stop cushion 45 secured by a fastening screw 46 to the support block 22-. In this retracted position as shown in FIG. 6, both the sharpened cutting edge 43 "and the thread engaging hook 44 v occupy positions radially outwardly of the loop taker 12. Both of the bell crank levers 24 and 25 are provided with lever arms 24' and-25', respectively, by which the levers may be imparted shifting movements. At a point spaced from the fulcrum stud 23, the support block 22 accommodates an eccentric end portion 49 of a pivot pin 50 preferably clamped by a setscrew 51. On the pin 50 is pivoted a thread pull-off lever 52. The thread pull-off lever 52 is formed with a lateral stop arm 53 engageable with an abutment pin 54 projecting from the bell crank lever 24. The thread pull-off lever 52 is also formed with a shoulder 55 engageable with the flattened heel 42 of the thread catching arm. A coil spring 56 on the pivot pin 50 has one extremity anchored on the support block 22 and is formed at the other extremity 57 for engagement with the thread pull-off lever 52 so as to bias the pull-off lever in a counterclockwise direction as viewed in FIGS. 6, 7 and 8 against either the abutment pin 54 or the heel 42 of the thread catching arm whichever is shifted most in a clockwise direction. The free extremity of the thread pull-off lever 52 is formed with a laterally offset thread engaging finger 58 as shown in FIG. which in the retracted position of the parts illustrated in FIG. 6, is located radially outward of the loop taker 12.

The hook 44 of the thread catching arm and the lateral finger 58 of the pull-off lever, to unerringly engage the sewing threads, move preferably in paths overlapping the paths of axial projections of elements on the loop taker. The actuating mechanism for shifting the elements of the thread trimming mechanism in such a way that interference with the loop taker is avoided, will now be described.

As shown in FIG. 1, the actuating mechanism of the sewing machine includes a shaft 60 journaled in the bed 11 and connected as by means of a timing belt 61 with other actuating mechanism in the sewing machine. By means of gears62, a hook shaft 63 to which the loop taker 12 is secured, is driven preferably at a speed of two revolutions for each revolution of the bed shaft 60.

Two cam elements for operating the thread trimming mechanism are carried by the bed shaft. A first cam 70, which is secured by a set screw 71 to the bed shaft, is shown in FIGS. 2 and 3. The first cam includes a hub 72 from which projects a cam lobe 73 which extends only approximately 180 about the bed shaft. The periphery of the cam. lobe is formed with cam surfaces 74 and 75 disposed at different distances radially from the bed shaft axis. Also extending from the hub 72 is a radial arm 76 terminating in a follower throw-out plow 77 which may be arranged diametrically opposite to the cam lobe 73.

A second cam 80 formed with a hub 81 is similarly secured to the bed shaft 60 by a set screw 82 and includes a cam lobe 83 which extends only approximately 180 about the bed shaft 60. In the embodiment for the loop taker illustrated in the accompanying drawings, the cam lobe 83 of the second cam is formed to extend at a constant distance radially from the bed shaft axis. It will be appreciated that the peripheries of both the first and second cam lobes may be varied to suit the requirements of any particular loop taker for which it is desired to adapt this trimmer v In FIG. 4 of the drawings, both the first and second cams 70 and 80 are shown to indicate the relative ar-- rangement on the bed shaft 60.

The follower 90 for the first cam 70 is formed at the extremity of a rock arm 91 secured by a split clamp 92 to a rock shaft 93 which is axially shiftable as well as 93 is connected to an electric solenoid 95 which when energized draws the follower 90 into the path of the cam lobe 73 of the first cam. A light return spring 96 urges the follower into retracted position, but this spring is preferably so small that while the cam lobe 73 is effective, the friction prevents the spring 96 from acting. The plow 77 will retract the follower and the spring serves primarily to prevent accidental shift of the follower toward the first cam.

An elongate crank pin 97 on the rock shaft 93 provides a connection with a link 98 which will not separate on axial movement of the rock shaft. The link 98 is pivoted in turn to a rock arm 99.clamped on a rock shaft 100 which extends forwardly in the sewing machine bed 11 through the web 20 where a rock arm 10] is secured thereon. I

The rock shaft 100 extends in telescopic fashion through a rock sleeve 109 journaled in the web 20. A follower arm 110 for the second cam 80 is secured to the rock sleeve at one side of the web 20 and a rock arm 111 is .secured to the rock sleeve adjacent to the rock arm 101.

A connecting link 115 is provided between a pivot pin 116 in the rock arm 111 and a pivot pin 117 in the lever arm 24' of the bell crank 24 to which the thread cutting blade 26 is secured.

Aconnecting link 120 is also provided between a pivot pin 121 in the rock arm 101 and a pivot pin 122 in the lever arm 25' of the bell crank 25 to which the thread catching arm 40 is secured. The connecting link 120, however, is formed with an extension 123. beyond the pivot pin 122 to which extension is secured a coil spring which is attached to an anchor pin 131 located on the rock arm 111 between the sleeve 109 and the pivot pin 116.

Because of this arrangement of the spring 130, tension in the spring will cause it to bias the parts of the thread trimming mechanism into the retracted position shown in FIG. 6. In this retracted position, not only will the thread engaging elements of the thread trimmer be positioned radially outwardly of the loop taker, but the follower 90 for the first cam 70 will be urged toward the axis of the bed shaft 60 while the follower arm 1 10 for the second cam 80 will be urged away from the axis of the bed shaft 60 and in a retracted position out of the path of the second cam lobe 83.

OPERATION cause one additional rotation of the sewing machine bed shaft 60.

Preferably, the solenoid 95 draws the follower 90 for the first cam 70 into the path of the cam 70 when the follower 90 occupies a position beyond the approximate occupied by the cam lobe 73. As the bed shaft 60 turns, therefore, the follower 90 will be shifted radially outward by the cam surface 74 of the cam lobe 73 causing the thread picking arm 40 tomove radially inwardly across the path of the loop taker pull-off rib carrying with it the thread engaging finger 58 of the 'thread pull-ofi' lever 52 into the position shown in FIG.

7. These movements may be timed to occur without 7 beyond the follower arm 1 10 thus to control movement of the thread cutting blade 26 into cutting position toward the loop taker as shown in FIG. 8. The pin 53 on the bell crank 24 will engage the lateral stop arm 53 on the thread pull-off lever 52 causing further movement of the thread engaging finger 58 completing the thread pull-off action.

At this time during the operation, the increased radius segment 75 of the first cam 70 causes an additional increment of movement of the thread catching arm 40 to insure pick up of both the bobbin and needle thread limbs to be severed. It will be appreciated that the location and shape of these cam surfaces may be chosen to impart these movements of the parts to the extent and at such times as will avoid interference with the operating parts of the loop taker.

As the bed shaft 60 continues to rotate, the follower 90 is moving radially inwardly from the cam surface 75 to the cam surface 74 will cause the thread catching arm to retract into thread severing relation with the thread cutting blade as shown in FIG. 9.

Shortly thereafter, on continued rotation of the bed shaft 60 the first cam 70 will move out of engagement with the follower 90, thus allowing the parts to return to the position shown in FIG. 6 in which position the,

sewing machine having a circularly moving loop taker for concatenating a needle thread with thread from a bobbin within said loop taker, said loop taker having an exposed axial face, and an actuating mechanism for operating said loop taker, said thread trimming mechanism comprising a plurality of thread influencing members each separately supported for movement transversely of the face of said circularly moving loop taker, a plurality of different cam means carried by said sewing machine, a separate cam follower means cooperating with each of said cam means, operative connections between each of said cam follower means and different ones of said plurality of members of said thread trimming mechanism, and drive means operated by said actuating mechanism for moving said cam means relatively to each of said separate cam follower means at a different time during the circular movement of said loop taker so as to move said different ones of said plurality of members of said thread trimming mechanism transversely of the face of said circularly moving loop 45 I taker at different times during the'circular movement of saidloop taker.

2. A thread trimming mechanism as set forth in claim 1 in which said thread influencing members of said thread trimming mechanism include a thread catching arm and a thread cutting blade, and in which said cam means includes a first cam, linkage operatively connecting the cam follower associated with said first cam with said thread catching arm, a second cam, and linkage operatively connecting the cam follower associated with said second cam with said cutting blade and in which said drive means is arranged to move said first cam into cooperative relation with thecam follower associated with the thread catching arm before said second cam is moved into cooperative relation with the cam follower associated with said cutting blade.

3. A thread trimming mechanism as set forth in claim 2 in which said thread influencing members include a bobbin thread pull-off arm, means for biasing said bobbin thread pull-off arm away from said loop taker, and interengaging drive means on said bobbin thread pulloff arm and on both said thread catching arm and said thread cutting blade for shifting said bobbin thread pull-off member in opposition to said biasing means.

4. A thread trimming mechanism as set forth in claim 2 in which both said first and second cam means comprise cam discs formed with peripheral cam surfaces and in which spring means is provided for biasing said thread catching arm and said thread cutting blade into retracted positions remote from said loop taker, the cam follower associated with said first cam means being positioned by said linkage closer to the axis of said first cam than the maximum radius of said peripheral cam surface thereof when said thread catching arm occupies said retracted position, the cam follower associated with said second cam means being located by the linkage in a position at a greater distance from the axis of said second cam means than the maximum radius of said peripheral cam surface thereof when said thread cutting blade occupies said retracted position, means for selectively shifting said cam follower into tracking relation with said first cam means, and spring means extending between said thread catching arm and said thread cutting blade and effective to shift said cam follower into tracking relation with said second cam means after said thread catching arm is shifted by said first cam means. 

1. A thread trimming mechanism for a lockstitch sewing machine having a circularly moving loop taker for concatenating a needle thread with thread from a bobbin within said loop taker, said loop takEr having an exposed axial face, and an actuating mechanism for operating said loop taker, said thread trimming mechanism comprising a plurality of thread influencing members each separately supported for movement transversely of the face of said circularly moving loop taker, a plurality of different cam means carried by said sewing machine, a separate cam follower means cooperating with each of said cam means, operative connections between each of said cam follower means and different ones of said plurality of members of said thread trimming mechanism, and drive means operated by said actuating mechanism for moving said cam means relatively to each of said separate cam follower means at a different time during the circular movement of said loop taker so as to move said different ones of said plurality of members of said thread trimming mechanism transversely of the face of said circularly moving loop taker at different times during the circular movement of said loop taker.
 2. A thread trimming mechanism as set forth in claim 1 in which said thread influencing members of said thread trimming mechanism include a thread catching arm and a thread cutting blade, and in which said cam means includes a first cam, linkage operatively connecting the cam follower associated with said first cam with said thread catching arm, a second cam, and linkage operatively connecting the cam follower associated with said second cam with said cutting blade and in which said drive means is arranged to move said first cam into cooperative relation with the cam follower associated with the thread catching arm before said second cam is moved into cooperative relation with the cam follower associated with said cutting blade.
 3. A thread trimming mechanism as set forth in claim 2 in which said thread influencing members include a bobbin thread pull-off arm, means for biasing said bobbin thread pull-off arm away from said loop taker, and interengaging drive means on said bobbin thread pull-off arm and on both said thread catching arm and said thread cutting blade for shifting said bobbin thread pull-off member in opposition to said biasing means.
 4. A thread trimming mechanism as set forth in claim 2 in which both said first and second cam means comprise cam discs formed with peripheral cam surfaces and in which spring means is provided for biasing said thread catching arm and said thread cutting blade into retracted positions remote from said loop taker, the cam follower associated with said first cam means being positioned by said linkage closer to the axis of said first cam than the maximum radius of said peripheral cam surface thereof when said thread catching arm occupies said retracted position, the cam follower associated with said second cam means being located by the linkage in a position at a greater distance from the axis of said second cam means than the maximum radius of said peripheral cam surface thereof when said thread cutting blade occupies said retracted position, means for selectively shifting said cam follower into tracking relation with said first cam means, and spring means extending between said thread catching arm and said thread cutting blade and effective to shift said cam follower into tracking relation with said second cam means after said thread catching arm is shifted by said first cam means. 